1. Field of the Invention
This invention relates to a magnetic detecting element and, more particularly, to a magnetic detecting element for detecting an external magnetic field by utilizing a magnetic impedance effect.
2. Description of the Related Art
Although the recent magnetic sensor has become diversified with rapid development of an information equipment or a measuring/controlling equipment, miniaturization and high precision of the magnetic sensor are expected in the future. In the field of a magnetic head, a digital magnetic recording equipment is miniaturized. For example, in a hard disk drive serving as an external storage device of a computer or a digital compact cassette recorder (DCC) serving as a digital audio equipment, since an S/N ratio decreases due to decreases in track width and relative speed in a conventional induction type magnetic head, a magnetoresistive effect element (to be referred to as an MR element hereinafter) is used as a reproducing head. However, the MR element has no speed dependency of a medium, and is suitable for output extraction at a low speed, but the MR element has a resistance change rate of only several %. For this reason, development of a higher-sensitivity element is demanded for high-density integration in the future.
In the field of a sensor such as a magnetic encoder, a magnetic flux leaking outside becomes externally small by decreasing a magnetizing pitch of an adhered magnetic material, and low sensitivity poses a problem even in an MR element.
Recently, a magnetic detecting element utilizing a magnetic impedance (to be referred to as MI hereinafter) effect disclosed in Japanese Laid-Open Patent Application No. Hei 6-281712 has attracted attention. This uses the following phenomenon. That is, a high-frequency current of an MHz band flows in a wire made of magnetic material, and magnetization in a state where the magnetic domain wall of circular magnetization does not easily move is rotated by applying an external magnetic field, thereby largely changing permeability. A change in permeability causes a change in impedance.
Merits of such an element are as follows. That is, the element is free from the influence of a diamagnetic field because the element does not excite in the longitudinal direction of a magnetic material, and is suitable for miniaturization because the length of the element can be shortened to be about 1 mm or less. The element obtains a high resolution of flux detection of 10.sup.-5 Oe!, while an MR element obtains a low resolution of flux detection of 0.1 Oe!. In addition, while an MR element obtains an amount of change in impedance of about 3%, the element utilizing the MI effect obtains a several 10%-order change in impedance.
Since the element utilizing the MI effect has an impedance whose inductance component largely changes, the element is incorporated as an inductor L of a Colpitts oscillator shown in FIG. 1 or a multivibrator oscillator shown in FIG. 2. In that instance, a change in inductance caused by an external magnetic field is converted by amplitude modulation, and is then outputted after being subjected to frequency detection.
The functions of the element utilizing the MI effect have been found in an amorphous wire. The amorphous wire has excellent productivity as a material. However, when the amorphous wire is applied to a magnetic sensor, if the wire has a circular section having a diameter of several 10 microns, the wire cannot be easily handled.
More specifically, since the wire has the circular end portion having a several 10 microns with respect to a recording medium having a recording wavelength of several microns or less, the element cannot absorb a flux due to a shaping loss at the end portion. In addition, since the wire having a diameter of several 10 microns can be easily bent, handling such as alignment of elements cannot be easily performed.
For this reason, if a magnetic detecting element utilizing the MI effect can be constituted by a thin film, the element can be suitable for miniaturization because the thickness, width, and length on the substrate can be freely selected. However, in order to constitute the element by a thin film, the following points are required.
1) An MI effect which has quality higher than that of an amorphous wire is obtained. PA1 2) The element has static characteristics (high Q (quality factor) value) so that the element can be incorporated in an oscillation circuit.